Nicotine, and cotinine concentrations in serum and

Transcription

1 Br. J. clin. Pharmac. (1984), 18, 915, and cotinine concentrations in and of nursing smokers W. LUK & H. NAU* Institut fur Toxikologie und Embryonalpharmakologie, Freie Universitat Berlin, Garystrasse 9, D1 Berlin 33, F.R.G. 1 Analysis of 44 samples from 3 nursing smokers revealed that there was a linear correlation between nicotine concentrations in and in (r =.7). The nicotine concentrations in were considerably higher than the corresponding concentrations: / concentration ratio = ; (n = 44). There was also a linear correlation between the cotinine concentrations in and in (r =.89). The cotinine concentrations in were lower than the corresponding concentrations: / concentration ratio = ; (n = 44). 3 The direct comparison between the halflives of nicotine in and in was possible in five nursing smokers. The halflife of nicotine in was determined in four additional smoking mothers. The halflife of nicotine in t½, = 97 + min slightly exceeded the halflife of nicotine in ti1 = min; the difference between these two values was not statistically significant (P >.5). 4 otinine concentrations remained fairly consistant during a 4 h interval without smoking. Keywords nicotine cotinine smoking Introduction A number of studies indicate that 35% of nursing mothers are smokers (Kuzma & Kissinger, 1981; The health consequences of smoking, US Department of Health, Education and Welfare, 1973). These smoking mothers, like all smokers, inhale thousands of different substances with every puff, including numerous toxic substances (Schmeltz et al., 1975). Little is known about the content of exogenous and potentially harmful substances in derived from tobacco smoke. In a number of earlier studies nicotine concentrations have been assayed in by semiquantitative bioassay techniques (Emanuel, 193; Hatcher & osby, 197; Perlman et al., 194; Thompson, 1933). In some more recent studies nicotine as well as its major metabolite cotinine have been measured in of nursing smokers as well as passive smokers by specific * Author for correspondence analytical assay methods using gas liquid chromatography (Ferguson et al., 1976; Hardee et al., 1983). In these studies, however, single samples of a limited number of mothers have been investigated only. omparative measurements in samples of the mothers have not been performed. Therefore, little is known on the time course of nicotine and cotinine concentrations in and on the extent of transfer of nicotine and cotinine from into. Particularly the important question of possible accumulation of nicotine and cotinine in has not yet been adequately addressed. The pharmacokinetics of nicotine as well as cotinine have been extensively studied in of smokers during the past few years (Benowitz et al., 198; Isaac & Rand, 197; Kyerematen et al., 198, 1983; Langone & van Vunakis, 1975; Russell & Feyerabend, 1978). To gain detailed information on nicotine and cotinine concentrations in of nursing smokers we have investi 9

2 1 W. Luck & H. Nau gated both the extent of transfer of nicotine and cotinine from into and have compared the halflives of nicotine and cotinine in with corresponding halflives in. A specific gas chromatographic assay technique has been used for nicotine and cotinine determinations. The halflives were determined during a 4 h time interval where the mothers refrained from smoking. During this interval multiple and samples have been collected. Methods The samples (volumes 5 ml) have been collected by the smoking mothers by pressure on the breast or by pumping the into sterile plastic tubes. The samples were frozen at until analysis. The time difference between the collection of the samples and of the venous blood samples (1 ml) was always less than 5 min. The blood samples were centrifuged at 3 rev/ min, the was stored at until analysis. The transfer of nicotine and cotinine from into was investigated in two series of experiments. In the first series a single sample and at the same time a single sample were collected from each of 18 nursing smokers. The time difference between the last cigarette smoked and the collection of the samples was between.5 h and 4. h. The number of cigarettes smoked by these 18 mothers ranged from 54 cig/day. In the second series the halflives of nicotine and cotinine were determined in and of five nursing smokers. These five mothers smoked until the initiation of the experiment ( h) the usual number of cigarettes. Then, the mothers abstained from smoking, and and samples were collected at hourly intervals for a period of 4 h. The time difference between the last cigarette smoked and the first and sample was at least 15 min to assure that the distribution equilibrium between the nicotine concentrations in and had been reached. From one mother an additional and sample was collected 1 min after the first cigarette had been smoked at the end of the experiment to gain further insight into the transfer rate of nicotine from to. In both series of experiments 44 / sample pairs have been collected of 3 smokers. In four additional smokers nicotine and cotinine concentrations in were measured during a 4 h interval where the mothers had abstained from smoking to gain additional data on the halflife of nicotine and cotinine in. and cotinine were extracted from (aliquots of 1 ml) according to methods previously reported (Hengen & Hengen, 1978; Feyerabend & Russell, 1979). The nicotine and cotinine concentrations were then measured by gas liquid chromatographic (g.l.c.) procedures. The conditions of chromatography were set for nicotine as follows: glass column (6 mm diameter x mm length), packed with 1% Apiezon and % KOH on hromosorb WAW mesh 8/1 (Feyerabend & Russell, 1979). Temperature of the injector: 4, temperature of the oven: 3, temperature of the PNdetector: 3. Ncarrier gas flow: 3 ml/min. Intetnal standard: modaline (Hengen & Hengen, 1978). The retention times for nicotine and modaline were.9 and 1.3 min respectively. The limit of detection for nicotine was. ng/ml. Standard curves were linear over the entire concentration range studied,.5 ng/ml. For the determination of cotinine a specific g.l.c. method was developed: a glass column (6 mm diameter, m length), packed with polys 179 (Applied Science) was used. Temperature of thi injector: 3(, temperature of the oven: 8, separation with temperature programme: 8 /min, temperature of the PNdetector: 3. Ncarrier gas flow: 3 ml/min. Internal standard: lignocaine (Feyerabend & Russell, 198). The retention times for lignocaine and cotinine were.9 and 1. min respectively. The limit of detection for cotinine was 5 ng/ml. Standard curves were linear over the entire concentration range studied, 55 ng/ml. Results The range of nicotine and cotinine concentrations as well as the / concentration ratios found in the 44 / sample pairs are reported in Table 1. The data shown in Table 1 indicate that the / concentration ratios of nicotine varied much more than those of cotinine. In Figures la and b the nicotine and cotinine concentrations in the of the smoking mothers were plotted against the corresponding concentrations. There was a linear correlation between the nicotine and cotinine concentrations in and in (nicotine: r =.7, cotinine: r =.89). The nicotine concentrations in were higher than those in, while the cotinine concentrations in were lower than those in. All / concentration ratios of nicotine exceeded 1, while for cotinine most / concentration ratios were below 1. Further, there was no correlation between the

3 Table 1 and cotinine in and and cotinine concentrations in and of nursing smokers Patients Samples otinine (n) (n) (ng/ml) (ng/ml) Serum ' Milk ' 1 1 Milk/ concentration ratio ( )' (.6 1.)' 1 range mean + s.d. 11 / concentration ratios and the time interval between the last cigarette consumed and the collection time. This indicates a rapid distribution of nicotine and cotinine between and. The time course of nicotine and cotinine concentrations in and in of five smoking mothers during a 4 h time interval without cigarette smoking is shown in Figure. The time course of nicotine and cotinine concentrations in of four additional nursing smokers during a 4 h time interval is shown in Figure 3. The decay of nicotine concentrations in and followed first order kinetics and allowed graphic determination of halflives in both fluids (Table ). The halflives in, t½/ = 97 ± min, slightly exceeded those in, t½ = min. There was no statistically significant difference between halflives of nicotine in and (P >.5, Student's ttest). The cotinine concentrations in and did not decrease sufficiently during these 4 h time intervals to allow determination of the halflife of this substance. a / 6 5 I 4 ED cn c) ) 1 /! 1. r =.7 slope =.9 1 io 3 Serum concentration (ng/mi) 4 b 31 E cm c o W.) r =.89 slope = Serum concentration (ng/mi) Figure 1 oncentration of (a) nicotine and (b) cotinine in against corresponding concentrations in nursing smokers. 4

4 1 W.Luck&H.Nau D c 1 o D cj 5 ri t M.B. u otinine =8 minm /O ~ t%=86min last cigarette Time (h) 1 E 5 S c 'r. 1 8 E.D. _ A L otinine t%=81 min ti=73 mm I I LI I last cigarette Time (h) 1 E 5 *ve o 1 r 5 8.S. ;t otinine t,=7 min 4 I last cigarette Time (h) M.J. 1 E 5 E *._ 1 co 5 74 min _ t=9 min last cigarette Time (h) one cigarette otinine 5 1 c 5. 1 E.L. ik ~~~~~ otinine t=1min /m,ilk 5 t=75 m erum I I last cigarette Time (h) Figure and cotinine concentrations in and of five smoking mothers (subjects E.L., M.B., M.J.,.S., E.D.) during a 4 h time period where no cigarettes have been consumed.

5 1 'E5 c ~ 5 otinine and cotinine in and Time after last cigarette (h) Figure 3 and cotinine concentrations in of four smokers (S.P. U, D.P. A, D.B. *, S.N. ) during a 4 h time interval where no cigarettes have been consumed. Discussion The considerable accumulation of nicotine in (Figure la, Figure ) can be explained by the chemical properties of this substance as well as the ph gradient between and. is a basic substance: pkal = 7.8, pka = 3.1 (Yamamoto, 1965) with low plasma protein binding: 4.9% (Rosenberg et al., 198) and good lipid solubility (Oldendorf, 1974). Therefore, nicotine would be expected to rapidly diffuse from to. The ph of is usually lower than the ph of and also varies considerably more than the ph of. While ph was reported to be (Documenta Geigy, 1975), the ph of was reported to vary between , with a mean Table Halflives of nicotine in and determined during a 4 h time interval of nonsmoking Subject ty½ ofnicotine (min) Serum Milk M.B E.L S E.D M.J D.B. n.d.' 96 S.N. n.d.1 17 S.P. n.d.' 1 D.D. n.d.1 7 Mean±s.d. 81±9 95± (n =5) (n = 9) 1 not determined Table 3 Milk/ concentration ratios for nicotine predicted for various ph values of. Serum ph 7.4 ph value of Milk/ concentration ratio value of (Ansell et al., (1977). If equilibrium between and can be assumed and the nonionized form of nicotine has reached equal concentrations in and, the ionized concentrations and therefore also the total concentrations of nicotine can be expected to be much higher in than in. The / concentration ratios can be predicted from the HendersonHasselbalch equation: In Table 3 such calculated / ratios are listed for a ph of 7.4 and a range of ph values for. The values of / concentration ratios predicted from the ph gradient between and (Table 3) agree well with values reported in the present study (mean + s.d. = ). The data in Table 3 show that small changes of the ph value of can result in considerable changes of the / concentration ratios. This strong dependence on the ph gradient explains the considerable range of the / concentration ratios for nicotine (1.456.). The simultaneous increase of nicotine concentrations in and in (see Figure, subject M.J.) after smoking a cigarette shows that nicotine is transferred rapidly from into. The similar decay of nicotine concentrations in and in shows that nicotine diffuses rapidly in both directions (Table and Figure ). Further proof for the importance of the ph gradient for the distribution of nicotine from into extravascular compartments has been presented by Russell & Feyerabend (1978). These authors found a simultaneous increase of nicotine concentrations in and in saliva. Because of the low ph of saliva (ph 5.5), nicotine cumulates considerably in this fluid (saliva/ = 1.7). The halflife of nicotine in saliva was, as found for in the present

6 14 W. Luck & H. Nau study, in the same range as those in (appr. 7 min). The time course of nicotine concentrations found in the present study agrees well with the previously reported data: the highest nicotine concentrations were found immediately after smoking. The decay of nicotine concentrations was found to be biphasic with a short distribution phase (t1i = 51 min) and a longer elimination phase showing considerable interindividual variation (tl,z = 714 min) (Benowitz et al., 198; Kyerematen et al., 1983; Rosenberg et al., 198; Russell & Feyerabend, 1978). The ratios of nicotine concentrations between and showed inter and intraindividual variation. In one case (Figure, subject E.L.), the / concentration ratio rose from.8 at the beginning of the experiment to 6. after 4 h; therefore, the halflife of nicotine in, t½ = 1 min, was considerably greater in this patient than the halflife in, t½, = 75 min. In the other four smokers these ratios remained relatively constant and therefore, halflives in and were very similar. hanges in the / concentration ratios of nicotine probably result from changes of the ph of. Little is known on the time course and regulation of ph in nursing mothers. Hall (1975) showed, that the ph increases during the course of one feeding meal by.1. units. Ansell etal. (1977) demonstrated great intraindividual daytoday variations of the ph values of. On the averagbe, the half life of nicotine in, t½, = 97 + min, (n = 9) were found to be only slightly longer than in, ty, = 81 ± 9 min (n = 5, see Table ). The relatively small variation of the / concentration ratios of cotinine can be explained as follows: this substance is a weak base. pkal = 4.5 (Yamamoto, 1965). Therefore, cotinine is present both in and in predominantly as a nonionized molecule. The ph difference between and is therefore not expected to influence the cotinine concentration in. otinine concentrations remained rather constant in of smoking mothers (see Figure ) which agrees with the findings of Kyerematen et al. (198). The low intraindividual variations of cotinine levels are the result of the prolonged half life of cotinine in of smokers, t½ = 63 h (Langone et al., 1975; Kyerematen et al., 198). The range of cotinine concentrations in was between 1433 ng/ml which agrees with the values reported previously in the literature (18 ng/ml) (Benowitz etal., 1983; Hill et al., 1983; Rickert et al., 1981). A comparison of nicotine and cotinine concentrations in found in our study (Table 1) with those reported previously in literature is only possible with the studies of Ferguson et al. (1976) and Hardee et al. (1983), because only in these two studies specific analytical assay techniques were used (gas liquid chromatography): Ferguson et al. (1976) reported nicotine concentrations in a range of <51 ng/ml in 8 samples of nine nursing mothers who smoked 13 cig/day. The nicotine concentrations in 6 of the 8 samples were in the range of <114 ng/ml; in two samples nicotine concentrations were 77 and 51 ng/ml, respectively. Hardee et al. (1983) reported nicotine concentrations in of three smoking mothers in a range of 15 ng/ml and cotinine concentrations in a range of 53 ng/ml. In the of passive smokers the nicotine concentrations ranged between 17 ng/ml and the cotinine concentration between 1 ng/ml. Serum nicotine concentrations within a range of 11 ng/ml have been reported in a number of previous studies. In the majority of smokers nicotine concentrations were below 6 ng/ ml, only in isolated cases nicotine concentrations reached 1 ng/ml (Armitage et al., 1975; Benowitz etal., 198; Isaac etal., 197; Russell & Feyerabend, 1978; Russell et al., 1975, 198). The / concentration ratios found in the present study as well as the maximum nicotine concentrations (1 ng/ml) which can be reached in of smokers indicate that the two highest values reported by Ferguson et al. (1976) (77 ng/ml and 51 ng/ml) should be considered as extreme values. In a previous study where we have analysed 39 samples the highest nicotine concentration in was 1 ng/ml (Luck & Nau, in preparation). It should be pointed out in this respect that contamination of samples, particularly by the fingers of the smoking mothers, must be assiduously avoided in such studies. In conclusion, we have found a linear correlation for the concentrations of both, nicotine and cotinine, between and of nursing smokers. concentrations are considerably higher in than in (/ concentration ratio = ) and cotinine concentrations were lower in than in (/ concentration ratio = ). The rapid transfer of nicotine from into and the short halflives of nicotine in indicate, that mothers who cannot refrain from smoking during the nursing period, should attempt to prolong the time between the last cigarette smoked and breast feeding to minimize exposure of the nursing infant by this substance. This work was supported by a grant from the Deutsche Forschungsgemeinschaft to the SFB 9. The preparation of the manuscript by Mrs R. Ebbinghaus and the artwork by Mrs h. Duerkop is gratefully acknowledged.

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